The present invention relates to a device for detecting the rotational angle of a rotor.
Various types of systems for improving traveling stability, such as a vehicle stability control system and an electronic control suspension system, are installed in recent vehicles. These systems execute control to stabilize the attitude of the vehicle in accordance with the steering angle of the steering wheel. The rotational angle of the steering wheel is detected by a rotational angle detector, which is incorporated in a steering column of the vehicle.
Japanese Laid-Open Patent Publication No. 2004-309222 describes an absolute angle detection type rotational angle detector, which detects the absolute value of the rotational angle (steering angle) of the steering wheel. The rotational angle detector includes a drive gear rotated integrally with the steering shaft and two driven gears mated with the drive gear. A magnet rotates integrally with each driven gear. The two driven gears have a different number of teeth. Due to the different number of teeth, the driven gears have different rotational angles when the drive gear rotates. The rotational angle detector includes two magneto-resistive elements MRE (FIG. 9) respectively arranged in correspondence with the two driven gears.
Each magneto-resistive element MRE provides a controller with a first analog signal and a second analog signal in correspondence with the rotational angle of the drive gear. The first analog signal is a sinusoidal wave signal, with each cycle of the sinusoidal wave corresponding to the rotation of the drive gear for a predetermined angle. The second analog signal is a cosine wave signal, with each cycle of the cosine wave corresponding to the rotation of the drive gear for a predetermined angle. The controller calculates the absolute value for the rotational angle of the drive gear from the first analog signal and the second analog signal. Thus, the controller readily obtains the present rotational angle when the power goes ON regardless of the steering wheel being rotated and changing rotational angle from the rotational angle detected when the power went off.